1. Field of the Invention
The present invention relates to a far-infrared emission powder with antibacterial activity, which can be applied to steel plates to provide antibacterial activity and far-infrared emission properties therefor. Also, the present invention relates to a steel plate which shields electromagnetic waves at low frequencies and can be used where antibacterial activity and far-infrared radiations are required.
2. Description of the Prior Art
Belonging to infrared radiations, far-infrared radiations have wavelengths of as long as 2.5xcx9c20 xcexcm. At higher than 0 K, far infrared radiations are generated from all materials, but extensively emitted especially from certain ceramics, so-called far-infrared emitters. So high in energy efficiency are far-infrared radiations owing to their transportation of energy through radiation that they are utilized in a broad spectrum of applications, as disclosed in Korean Pat. Publication No. 95-8584.
For instance, knowledge of the beneficial effect of far-infrared radiations on the body allows the application of far-infrared emitters to sauna construction, electric appliance, general construction, etc.
Representative of far-infrared emitters are jade and elvan, as disclosed in Korean Pat. Application Nos. 88-1616 and 95-26761. Besides, transition metal oxides are known to be high in far-infrared emissivity (Korean Pat. Publication No. 95-8584). Electromagnetic shield capacity cannot be expected from these far-infrared emitters because they have almost no conductivity and permeability.
There are various methods for introducing far-infrared emitting capacity to steel plates. For example, steel plates are coated with far-infrared emitting ceramic to improve their thermal resistance and energy efficiency as disclosed in Japanese Pat. Laid-Open Publication No. 2000-171045. Stainless steel plates can be made into far-infrared emitters by corrosion, as disclosed in Korean Pat. Application No. 90-22365. Korean Pat. Laid-Open Publication No. 1998-83239 introduces a method for making far-infrared emitting steel plates, in which a thermosetting resin such as a polyethylene resin is added with a zeolite powder containing far-infrared emitting ceramics such as Al2O3, SiO2, etc., and thermally treated. However, the steel plates show a far-infrared emissivity of only less than 0.90 over the whole wavelength ranges because unsuitable far-infrared emitters are selected. Particularly, their far-infrared emissivity is only on the order of 0.5-0.8 in the wavelength band ranging from 5 to 8 xcexcm, which is known to be beneficial to the health of the body.
Referring to FIGS. 4a and 4b, there are emission curves are displayed. Emissivity of conventional PCM (pre coated metal) steel plate are plotted versus wavelengths in FIG. 4a. FIG. 4b shows typical emission power of PCM steel plate and an ideal body and are plotted versus wavelengths. As seen in the curves, these steel plates do not show high efficiency far-infrared emission. Additionally, these steel plates are not expected to shield electromagnetic waves at low frequencies.
As conditions demand, steel plates are required to be inhibitory against microbes, as well as showing high far-infrared emissivity. In this regard, many prior arts suggest that antibacterial materials are applied to steel plates for use in interior finishes, kitchenware, etc. For example, Korean Patent Application No. 1996-58162 discloses silver (Ag) impregnated in a phosphate material as an antibacterial material applicable to steel plates. Likewise, inorganic materials of antibacterial activity such as Zn and Ag are impregnated in zeolite carriers that are of far-infrared emission, as disclosed in Japanese Pat. Laid-Open Publication No. Hei. 8-257493 and Korean Pat. Laid-Open Publication No. 1998-83239. Another example of the antibacterial materials applicable to steel plates is a photocatalyst such as TiO2 (Japanese Pat. Laid-Open No. 2000-63733). Further, U.S. Pat. No. 6,313,064 utilizes the catalytic activity of metal in combination with TiO2 in allowing for the antibacterial activity of steel plates. Most of the conventional antibacterial materials applied to steel plates are based on the antibacterial activity of metal ion and optical properties of TiO2. However, the carriers containing antibacterial metal ion and photocatalysts are very expensive in addition to being poor in far-infrared emissivity.
Consisting of time-varying electric and magnetic fields which interact differently with biological systems, electromagnetic waves were found to have detrimental effects on the body, which has led to the development of various methods and materials for shielding electromagnetic waves. Artificial waves adversely affecting the body are collectively called harmful waves.
Recent studies have demonstrated harmful effects of electromagnetic waves at low frequencies on biological systems. Particularly, a series of studies which revealed the interrelation of the electromagnetic field (60 Hz) around power transmission lines and carcinogenesis has had great repercussions all over the world.
In addition to carcinogenic effects, low frequency waves with magnetic properties were found to cause inductive currents in the body upon exposure to the waves for a long period of time, upsetting the biological balance of various ions, such as Na+, K+, Clxe2x88x92 and so forth, across cellular membranes, which adversely affects the hormone secretion and immunocytes of the body. A study has been reported that a magnetic field changes secretion amount of melatonin related with sleep and thus brings insomnia in long-term health effect.
Recent legislation, in response to environmental concerns stemming from adverse health effects of electromagnetic fields, has been enacted to lower the acceptable levels of electromagnetic waves emitted from various electrical or electromagnetic appliances in many countries. Further, the regulation concerning electromagnetic waves is used as an import barrier against electric and/or electromagnetic appliances. For example, Sweden and other European countries prohibit the import of TVs or computer monitors that show a magnetic leakage of 2 mG or higher.
Likewise, with electromagneticity related academic societies (Korea Electromagnetic Engineering Society) and medical societies as central figures, Korean governmental and non-governmental organizations have made much effort to enact a law which regulates exposure limits of electric and magnetic fields (Journal of the Korea Electromagnetic Engineering Society Vol. 8, No. 2, 1997; White Paper on the Activity at National Assembly of the Committee on the Problems of Harmful Electromagnetic Waves, issued December 1999; xe2x80x9cEpiodemiological Investigation for the Influence of Electromagnetic Waves on the Body and Study on the Enactment of Law Regulating Electromagnetic Wavesxe2x80x9d, Korea Radio Station Management Agency (KORA 99-09, August 2000).
In order to cope with such harmful electromagnetic waves, shielding technology has been developed in two aspects: construction and material. Copper and aluminum are currently in use as shields against electromagnetic waves. Also, the present inventors described a steel material with excellent magnetic shield effect at low frequencies in Korean Pat. Application No. 1999-52018. However, such non-iron materials and the steel plates with excellent electromagnetic shield capacity are not suitable as far-infrared emitters owing to their poor far-infrared emissivity.
Leading to the present invention, the intensive and thorough research, conducted by the present inventors, resulted in the finding that certain alkaline oxides have excellent far-infrared emissivity as well as inhibitory activity against microbes, and can be applied to steel plates.
Therefore, it is an object of the present invention to overcome the above problems encountered in the prior art and to provide a far-infrared emission powder which is of antibacterial activity with an alkaline pH in its saturate aqueous solution and shows far-infrared emission activity.
It is another object of the present invention to provide a resin-coated steel plate, which is of antibacterial activity and shows far-infrared emission activity.
It is a third object of the present invention to provide electromagnetic waves shielding steel plate coated resin containing far-infrared emission powder, which has shielding electromagnetic waves as well as antibacterial activity and far-infrared emission property.
In accordance with an aspect of the present invention, there is provided a far-infrared emission powder, which is of antibacterial activity with a pH value ranging from 7.5 to 10.5 in its saturated aqueous solution, and shows a far-infrared emissivity of 0.9 or higher.
In accordance with another aspect of the present invention, there is provided a resin-coated steel plate with antibacterial activity and far-infrared emission properties, having a resinous coating at a dry thickness of 5 to 60 xcexcm, said resinous coating comprising 5-100 parts by weight of a far-infrared emission powder per 100 parts by weight of a resin, said powder having a pH value ranging from 7.5 to 10.5 in its saturate aqueous solution, and showing a far-infrared emissivity of 0.9 or higher.